Influence of radiation therapy delay on abdominal tumor recurrence in patients with favorable histology Wilms’ tumor treated on NWTS-3 and NWTS-4: a report from the National Wilms’ Tumor Study Group

This study was undertaken to determine whether radiation therapy (RT) delay of ≥10 days had an adverse impact on abdominal tumor recurrence among children with favorable histology (FH) Wilms’ tumor enrolled in National Wilms’ Tumor Study (NWTS) 3 and 4. A total of 1226 patients with Stage II–IV FH tumors who received flank or abdominal RT in NWTS-3 and NWTS-4 were included in this analysis. Recurrent disease in the operative bed was classified as flank recurrence. Abdominal recurrence included all infradiaphragmatic tumor recurrences, including flank recurrences. This analysis included all flank/abdominal tumor recurrences, regardless of whether they might have been the initial or subsequent site of relapse. Based on the NWTS-1 results, RT delay was analyzed in two categories: 0–9 days and ≥10 days. The mean RT delay was 10.9 days; median delay was 9 days (range: 1–277 days). The RT delay was concentrated in a relatively narrow range of 8 to 12 days after nephrectomy in the majority of patients (59%). Univariate and multivariate analysis did not reveal RT delay of ≥10 days to significantly influence flank and abdominal tumor recurrence rates in NWTS-3 or NWTS-4. The 8-year flank tumor recurrence rates for 0–9 days and 10+ days RT delay were 1.9% and 1.2%, respectively ( p value = 0.3). The 8-year abdominal tumor recurrence rates for 0–9 days and 10+ days RT delay were 4.8% and 5.3%, respectively ( p value = 0.7). RT delay of ≥10 days did not significantly influence flank or abdominal tumor recurrence rates among children with FH tumors treated on NWTS-3 and NWTS-4. However, we were unable to test for a meaningful difference, because of the concentration of RT delay close to 10 days.